1. Field of the Invention
The invention relates to the field of processing workpieces in a plate press, in particular the loading of this plate press for the purpose of producing tempered particle board. In this connection it is of particular interest how the deposition of such a workpiece, for example of the particle board to be worked, on the press is performed, since the transfer from the loading device to the press must take place in such a way that the workpiece to be processed takes up as exact a position as possible in the press. This is achieved as a rule in that the workpiece to be processed is not placed with its entire surface on the press, but instead first with one edge and then with the other edge in order to prevent air cushion-like effects which lead to the floating of the workpiece on the press and therefore make the mentioned exact positioning worse, or respectively impossible.
Various systems for achieving this are known.
2. Prior Art
A loading device in accordance with the species is described in DE 28 47 273 C3, wherein clamping strips are provided as holding devices, which are opened and pulled outward in the deposited position of the workpiece to be processed, so that the workpiece can fall downward into the press (as a rule on the lower steam plate). The friction occurring when displacing the workpiece out of these opened clamping strips is intended to be prevented or at least minimized by providing additional placement rollers, on which the workpiece to be processed is placed when the loading strips are moved apart.
Another system (DE 35 03 156 C1) has the provision of doing without additional holding devices, such as clamping strips, for example, in this case the workpiece to be processed rests directly on the loading strips which are provided with holes, through which the workpiece to be processed is drawn in during the conveying process and through which an air flow is blown upward toward the workpiece during the placement process so that the workpiece floats on an air cushion.
A similar system is known from DE 39 14 866, wherein the loading device consists of belt conveyors which are moved into the pressing chamber, so that the workpiece to be processed is supported on its longitudinal edges by the belts of this belt conveyor system and conveyed into the press. When depositing the workpiece in the press, the two conveyor belts are pulled toward the exterior so that the workpiece can fall downward on the lower steam plate. In order to prevent the workpiece from being displaced toward the one or the other side by the left or the right conveyor belt because of uncontrolled friction, rollers at the inside of these conveyor devices are pivoted upward so that friction between the belt conveyor and the workpiece is reduced. However, this system is very elaborate since large masses (conveyor devices) must be rapidly moved, which requires a correspondingly large acceleration with corresponding great outlay of force and devices suitable for this.
It is common to the described loading devices that in spite of the mentioned additional devices it is not or not sufficiently assured that no sliding friction is created between the workpiece and the specific system respectively used for conveying and depositing, which extends underneath the workpiece and supports it. It is necessary in connection with the three systems mentioned at the outset that the workpiece always first be deposited with one side so that no air cushions form, on which the workpiece can float. With all known systems this has the result that the loading strips must be moved outward one after the other when depositing the workpiece, i.e. the second loading strip can only start its release movement when the first loading strip has already left the area of the workpiece and the latter has reached the press with the appropriate edge. This means in turn that the second loading strip must be retracted over the entire release path in order to let the other side of the workpiece drop on the lower steam plate. As a function of the outlay in machines for letting these processes take place as rapidly as possible, a certain length of time remains in which the workpiece is in contact with the hot steam plate, while the other edge area is still supported by the second loading strip and therefore is held above the steam plate. However, in connection with specific work processes in particular, for example when pressing resin-soaked papers which form a layered package, it is desirable to keep this length of time as short as possible, because otherwise processes will occur in the layered package (for example pre-condensation), which reduce the even quality of the workpiece.